Investigation of Thermodynamic Properties of Dimethyl Phosphate-Based ILs for Use as Working Fluids in Absorption Refrigeration Technology

In the current research, the binary solution containing ionic liquid (IL), 1-ethyl-1-methylmorpholinium dimethyl phosphate ([C1C2MOR][DMP]), 1-ethyl-1-methylpiperidinium dimethyl phosphate ([C1C2PIP][DMP]), or N,N,N-triethyl-N-methylammonium dimethyl phosphate ([N1,2,2,2][DMP]) with ethanol are investigated as new working fluids for absorption refrigeration technology. The IL was mixed with ethanol, which was considered as a refrigerant. Experimental (vapor + liquid) phase equilibria (VLE) of these binary systems were measured by an ebulliometric method within a temperature range from T = (328.15 to 348.15) K with an increment of 10 K and pressures up to 90 kPa. Experimental VLE data were correlated using non-random two-liquid (NRTL) within the maximum average relative deviation of 0.45%, which confirms the effectiveness of using such a model for calculations. Each of the proposed binary systems exhibit a negative deviation from Raoult’s law, which is a very important characteristic for working pairs used in absorption heat pumps or absorption refrigerators. From a technological point of view, measurements of physicochemical properties play an important role. In this research, liquid density and dynamic viscosity were determined at temperatures from T = (293.15 to 338.15) K at ambient pressure over the whole concentration range. These properties were correlated using empirical equations. From experimental density data, the excess molar volumes were determined and correlated using the Redlich–Kister type equation. Ionic liquid: [C1C2MOR][DMP] and [C1C2PIP][DMP] were synthesized and characterized using NMR analysis. The thermophysical characterization of pure ILs, including glass transition temperature (Tg) and heat capacity at the glass transition temperature (ΔgCp), was determined using the differential scanning calorimetry technique (DSC) at atmospheric pressure. In this work, the combination of basic studies on the effect of the cation structure of an ionic liquid on the properties of their solutions with ethanol and the possibility of future application of the tested systems in a viable refrigeration system are presented.


Introduction
With the need to conserve energy resources and protect the environment, the interest in absorption refrigeration equipment as an alternative to compressor units has grown significantly in recent years.
Absorption chillers are devices that make extensive use of thermal energy to produce cooling. These devices, using the so-called thermal compressor (absorber, pump, desorber system) for the process of compressing refrigerant vapors, are an ideal economic solution for unearned surplus technological or waste heat. They also work well where there is a shortage of electricity. Unlike compressor chillers, the generation of cooling in absorption devices does not require the supply of expensive electricity because the energy supply of the absorption device is heat in the form of hot water or steam (so-called waste heat).

DSC Measurements
The thermophysical properties of pure iLs were determined at a temperature range from T = (173.15 to 373.15) K with a 5 K·min −1 heating rate. The experimental data are collected in Table 1 and graphically presented in Figure 1. The list of available thermophysical data of the family of dimethyl phosphate-based iLs is presented in Table 1. The data shows that glass transition temperature was determined for all ion liquids, and the value of T g increases in the following series: [C 1 C 2 PYR][DMP] (T g = 189.7 K; ∆ g C p = 119. 6 Table 1, there are no comparisons between the experimental and literature data. The list of available thermophysical data of the family of dimethyl phosphate-based iLs is presented in Table 1. Table 1. DSC Analysis for the dimethyl-phosphate-based iLs: glass transition temperature, T g/ K, heat capacity at the glass transition temperature, ∆ g C p /J·mol −1 ·K −1 , temperature of (solid-solid) phase transition, T tr,1 /K, enthalpy of (solid-solid) phase transition, ∆ tr,1 H/J·mol −1 , melting temperature, T m /K and enthalpy of melting, ∆ m H/J·mol −1 measured using the DSC technique at atmospheric pressure (p = 0.1 mPa) a .
Molecules 2023, 28, 1940 4 of 33 are no comparisons between the experimental and literature data. The list of available thermophysical data of the family of dimethyl phosphate-based iLs is presented in Table  1.  Table 1. DSC Analysis for the dimethyl-phosphate-based iLs: glass transition temperature, Tg/K, heat capacity at the glass transition temperature, ΔgCp/J•mol −1 •K −1 , temperature of (solid-solid) phase transition, Ttr,1/K, enthalpy of (solid-solid) phase transition, Δtr,1H/J•mol −1 , melting temperature, Tm/K and enthalpy of melting, ΔmH/J•mol −1 measured using the DSC technique at atmospheric pressure (p = 0.1 mPa) a .

Tm/ (K)
where P is the pressure of the system; for component i: P S i represents the saturated vapor pressure; x i and y i are the liquid and vapor molar fractions; ϕ i is the fugacity coefficient in the gas phase; γ i is the activity coefficient in the liquid phase. Due to the low volatility of ionic liquids, the gas phase is assumed to consist only of solvent (ethanol) for IL systems.
Herein, y 2 is approximately equal to 1 and ϕ 2 is also approximately equal to 1 because of the relatively low pressure. Thus, Equation (1) can be further reduced to the following: Table 5. NRTL parameters fitted to experimental VLE data of {IL (1) + Ethanol (2)} with the average absolute deviation (AAD) and for the systems studied. Experimental data for each tested system shows a typical relationship that is a decrease in the vapor pressure of the ethanolic solution with an increase in the ionic liquid mole fraction. This has to do with the extremely low vapor pressure of a pure ionic liquid. Additionally, as the temperature increases, the vapor pressure in the studied systems increases.

NRTL Parameters %AAD
According to Equation (2), the experimental activity coefficient of ethanol (γ 2 ) in an IL-containing binary liquid mixture was calculated directly from the VLE data and is also presented in Tables 2-4. In each case, the determined values of the ethanol activity coefficient were below unity, indicating that the tested systems show negative deviations from the ideal behavior. This is due to the occurrence of stronger intermolecular interactions between IL and ethanol compared to (ethanol-ethanol) or (IL-IL) interactions. The negative deviation from Raoult's law is larger for higher IL mole fractions. It is worth mentioning that preferentially, IL used as an absorbent in absorption refrigeration technology should exhibit a powerful ability to absorb refrigerant (ethanol). Therefore, good working pairs are those presenting a highly negative deviation from Raoult's law. In this work, for each system presented here, the activity coefficients of ethanol (γ 2 ) are lower than unity; thus, each system presents a negative deviation from the ideal solution, which makes the working fluids proposed in this work potentially promising for applications in the area of interest undertaken.
A comparison of the VLE phase diagrams of {IL (1) + ethanol (2)} system under study at a temperature of 348.15 K within a pressure range up to 90 kPa and the vapor pressure of the ideal solution is shown in Figure 3. Such a comparison makes it possible to determine the effect of the structure of the cation of the ionic liquid on the vapor pressure, consequently, on the value and type of deviation of {IL + ethanol} systems from ideality. It was shown that among ethanolic systems investigated here, the vapor pressure increases in the following series: [N 1 (1) + ethanol (2)}. It is likely that in the case of an ammonium-based ionic liquid, intermolecular interactions between the ILs anion and ethanol play a key role. In addition, the short alkyl chains present in the cation of the ionic liquid promote stronger packing of alcohol molecules in the ionic liquid and the occurrence of van der Waals interactions. The weaker intermolecular interactions present in the case of an ionic liquid with a piperidinium cation are probably a consequence of its ring structure. It affects the formation of steric hindrance and weakens the interaction between IL and ethanol. In the case of the ionic liquid [C 1 C 2 MOR][DMP], the system shows the highest vapor pressure, therefore, the lowest deviation from ideality. It is speculated that the presence of an oxygen atom in the cation of the ionic liquid affects the occurrence of stronger interactions between ionic liquid molecules (IL-IL) than between the ionic liquid and the solvent (IL-ethanol).
Molecules 2023, 28,1940 10 of 33 A broader comparison of the effect of the ILs cation structure for the family of the dimethyl phosphate IL, taking into account the effect of the core structure and the presence of a hydroxyl group in the substituent on the vapor pressure of the {IL + ethanol} system is also shown in Figure 3. It was shown that for the presented family of the  [DMP]. The highest negative deviation from Raoult's law, thus, the strongest (IL-ethanol) interaction was determined in the case of IL with ammonium cation. A similar effect was observed for 1,3-dimethylimidazolium-and 1-ethyl-3-methylimidazolium cations. It was noted that the extension of the alkyl chain by one CH2 group in the imidazolium cation of IL has no significant effect on the vapor pressure in the studied system. This observation also holds true when increasing the core size of the cation from pyrrolidinium to piperidinium. Moreover, the vapor pressure in the system with [C1C2OHPYR][DMP] is significantly higher compared to the aliphatic analog, [C1C2PYR] [DMP]. It is speculated that the presence of a hydroxyl group in an ILs cation creates a greater possibility for a molecule to form hydrogen bonds between the molecules of the ionic liquid, thereby weakening the (IL-ethanol) interaction. Similarly, in the case of an ionic liquid with a morpholinium cation, the presence of an oxygen atom in the structure of the IL cation probably promotes the occurrence of stronger interactions (IL-IL) compared to (IL-ethanol) intermolecular interactions.
A broader comparison of the effect of the ILs cation structure for the family of the dimethyl phosphate IL, taking into account the effect of the core structure and the presence of a hydroxyl group in the substituent on the vapor pressure of the {IL + ethanol} system is also shown in Figure 3. It was shown that for the presented family of the DMP-based IL, the vapor pressure increases in the following series: . The highest negative deviation from Raoult's law, thus, the strongest (IL-ethanol) interaction was determined in the case of IL with ammonium cation. A similar effect was observed for 1,3-dimethylimidazolium-and 1-ethyl-3-methylimidazolium cations. It was noted that the extension of the alkyl chain by one CH 2 group in the imidazolium cation of IL has no significant effect on the vapor pressure in the studied system. This observation also holds true when increasing the core size of the cation from pyrrolidinium to piperidinium. Moreover, the vapor pressure in the system with [C 1 C 2OH PYR][DMP] is significantly higher compared to the aliphatic analog, [C 1 C 2 PYR][DMP]. It is speculated that the presence of a hydroxyl group in an ILs cation creates a greater possibility for a molecule to form hydrogen bonds between the molecules of the ionic liquid, thereby weakening the (IL-ethanol) interaction. Similarly, in the case of an ionic liquid with a morpholinium cation, the presence of an oxygen atom in the structure of the IL cation probably promotes the occurrence of stronger interactions (IL-IL) compared to (IL-ethanol) intermolecular interactions.
In our latest paper [31], it was shown that {[N 1,2,2,2 ][DMP] (1) + ethanol (2)} exhibit the highest vapor pressure among dimethyl phosphate-based IL. It was stated at the time that the ammonium cation substituted with alkyl groups is more aliphatic compared to the imidazolium cation, which prevents the formation of intermolecular hydrogen bonds with ethanol molecules. The small number of literature points under the considered temperature conditions (T = 348.15 K) prompted the authors of this work to conduct a more extensive study of VLE in this system. The experimental data compared with available literature data, is shown in Figure 3. The obtained results differ slightly from the literature data presented by Shen et. al. [40]. The reason for the reduction in vapor pressure in the {[N 1,2,2,2 ][DMP] + ethanol} system presented in this work is the water content of the pure ionic liquid. In the present work, the ionic liquid was synthesized in the laboratory, and the claimed water content is 8000 ppm, while Shen. et al. [40] declare the water content to be 664 ppm. From the literature studies [40] on VLE measurements in {water (1) + ethanol (2) + IL (3)} ternary systems, it is clear that an increase in water content results in a decrease in vapor pressure in the system.
Since the goal of the ongoing research is to search for working fluids alternative to the aqueous solution of lithium bromide, in addition to the vapor pressure data of {IL + ethanol} systems, Figure 3 also shows VLE data for {LiBr + water} system [55]. Although the tested iLs show a high ability to absorb ethanol, the vapor pressure under the same temperature conditions is higher than that of the commercially used system in refrigeration. It is worth considering the possibility of future use of ionic liquids as absorbents in cooling devices since they are designed compounds and exhibit several unique properties, and the commercially used systems are not without drawbacks. Apart from a few literature data for the ethanolic solution of ammonium-based IL, we have not found the literature data on (vapor + liquid) phase equilibria measurements for the systems analyzed in this work.
The NRTL equation for the excess Gibbs energy for the binary system is the following: where: where g 12 − g 22 = ∆g 12 and g 21 − g 11 = ∆g 21 are the binary interactions parameters. For isothermal data sets, temperature dependence of the parameters is represented as follows: For a complete T-P-x-y data set, a total of the following five parameters that is: From a developmental point of view, activity coefficients, γ i derived from excess Gibbs energies but in practice and in this work, the process is reversed and G E is tested from knowledge of activity coefficient.
The NRTL parameters were calculated by minimalized function given by the following: Molecules 2023, 28, 1940 11 of 30 The adjustable parameters of the following equation: ∆g A 12 , ∆g B 12 , ∆g A 21 , ∆g B 21 , α 12 = α 12 along with the average absolute deviation (AAD) given by the following equation: are listed in Table 5.
In graphical form, the experimental P-T-x data for {IL (1) + ethanol (2)} system together with the correlation results using the NRTL model are shown in Figures 2 and 3.

Density and Dynamic Viscosity Data
The liquid density and dynamic viscosity data of pure iLs: [DMP] and its ethanolic solution were investigated in a whole concentration range at a temperature within (293.15 and 338.15) K with an increment of 5 K. The experiment was performed under ambient pressure, and the experimental data are collected in Tables 6-8.      Temperature dependence of the liquid density for each system under study was described using the following equation: The root mean square error (RMSE) is expressed by The value of the parameters ρ 0 and α p along with RMSE are collected in Table 9.  The maximum RMSE value between the experimental density data and calculated values was determined to be 0.0003 for each binary system under study, which indicates excellent compatibility between these data. Experimental liquid density data versus temper-ature and composition for {[C 1 C 2 MOR][DMP] (1) + ethanol (2)} is presented in Figure 4 as an example. The solid lines presented in Figure 4a correspond to the results of calculations using Equation (10). The results for the other two systems are shown graphically in Figures  S3 and S4    The composition dependence of the liquid density for each system under study was described using a fourth-degree polynomial with the linear temperature dependence of the parameters of the polynomial.  Table 10.
The composition dependence of the liquid density for each system under study was described using a fourth-degree polynomial with the linear temperature dependence of the parameters of the polynomial.
The root mean square error (RMSE) is expressed by the following: The parameters of the polynomial described by Equation (12), together with the standard deviation, are collected in Table 10. The maximum σ value between the experimental and calculated density data was determined to be 0.03% for each binary system under study, which indicates excellent compatibility between these data. Experimental liquid density data versus composition for {[C 1 C 2 MOR][DMP] (1) + ethanol (2)} is presented in Figure 4b as an example. The solid lines presented in Figure 4b correspond to the results of calculations using Equations (12) and (13). The results for the other two systems are shown graphically in Figures S3 and S4 in Supplementary Materials.
Experimental density and viscosity data show that both pure iLs and their ethanolic solutions exhibit higher liquid density than ethanol, and, as expected, density and viscosity decrease with increasing temperature. This behavior is related to thermal expansion; the fluid density decreases and the intermolecular interactions become weaker due to the increase in the mutual distances between the molecules, and, therefore, the viscosity also decreases. Additionally, the addition of ethanol leads to a decrease in both mixture density and viscosity at each temperature.
Density and viscosity are fundamental physical properties of the solvent and tested medium and are extremely important in the design and optimization of any application, including absorption refrigeration technology, since they may be correlated with the medium fluidity and mass transfer. For this reason, both experimental studies and a discussion of values based on available literature data are warranted. We found no literature data for binary solution composed of ethanol and dimethyl phosphate-based iLs as well as the density of pure ionic liquids under study. Based on experimental and literature data for other dimethyl phosphate-based iLs, it was possible to discuss the effect of the cation structure on the liquid density of the ethanolic solution. The comparison of the experimental liquid density data for {[cation][DMP] (1) + ethanol (2)} system with the literature for other dimethyl phosphate-based ILs solutions at temperature T = 298.15 K is presented in Figure 5.  [41]. Points-experimental, or literature density data; solid lines-calculated using equation (12) with parameters given in Table 10; dashed lines-literature density data for {LiBr (1) + Water (2)} system [55].
The comparison shows the desirable characteristics of the studied systems from the point of view of future use as working fluids in absorption refrigeration technology because this liquid density value is lower than those for lithium bromide aqueous solution, commercially used as a working fluid in this area. It was shown that the liquid density of {IL (1) + ethanol (2) . The increase in the length of the alkyl chain in the imidazolium ring causes a decrease in density. The same trend is observed when the cyclic chain is increased from a five-member pyrrolidinium ring to a six-member piperidine ring. The presence of a hydroxyl group in the pyrrolidinium cation results in a significant increase in density. In addition, the presence of an oxygen atom in the morpholinium cation of the ionic liquid increases the density of the binary system with ethanol compared to the system with piperidinium-based IL.
From Figure 5, the ethanolic system with the ammonium-based ionic liquid shows the lowest density. These data, supplemented by the promising vapor pressure values presented earlier, allow us to conclude that the {[N1,2,2,2][DMP] + ethanol} system is the most promising for application in the area being undertaken.
Based on the liquid density data for pure compounds and the binary systems, the excess molar volumes ( ) for {IL (1) + ethanol (2)} solutions under study were calculated at each temperature. Obtained data are given in Tables 6 to 8. The temperature and composition dependence on the for each system under study is graphically presented in Figure 6.   [41]. Points-experimental, or literature density data; solid lines-calculated using Equation (12) with parameters given in Table 10; dashed lines-literature density data for {LiBr (1) + Water (2)} system [55].
The comparison shows the desirable characteristics of the studied systems from the point of view of future use as working fluids in absorption refrigeration technology because this liquid density value is lower than those for lithium bromide aqueous solution, commercially used as a working fluid in this area. It was shown that the liquid density of {IL (1) + ethanol (2) . The increase in the length of the alkyl chain in the imidazolium ring causes a decrease in density. The same trend is observed when the cyclic chain is increased from a five-member pyrrolidinium ring to a six-member piperidine ring. The presence of a hydroxyl group in the pyrrolidinium cation results in a significant increase in density. In addition, the presence of an oxygen atom in the morpholinium cation of the ionic liquid increases the density of the binary system with ethanol compared to the system with piperidinium-based IL.
From Figure 5, the ethanolic system with the ammonium-based ionic liquid shows the lowest density. These data, supplemented by the promising vapor pressure values presented earlier, allow us to conclude that the {[N 1,2,2,2 ][DMP] + ethanol} system is the most promising for application in the area being undertaken.
Based on the liquid density data for pure compounds and the binary systems, the excess molar volumes (V E ) for {IL (1) + ethanol (2)} solutions under study were calculated at each temperature. Obtained data are given in Tables 6-8. The temperature and composition dependence on the V E for each system under study is graphically presented in Figure 6. . Points-experimental results; solid lines-calculated using equation (14) with parameters given in Table 11.
For all systems under work, the value of is negative in the entire composition range at each temperature, which indicates the occurrence of stronger (IL-ethanol) compared to (ethanol-ethanol) or (IL-IL) interactions. The values can be explained by many contributions, such as contraction because of specific interactions between IL and ethanol or differences in molecule sizes.   (14) with parameters given in Table 11.
. For all systems under work, the value of V E is negative in the entire composition range at each temperature, which indicates the occurrence of stronger (IL-ethanol) compared to (ethanol-ethanol) or (IL-IL) interactions. The V E values can be explained by many contributions, such as contraction because of specific interactions between IL and ethanol or differences in molecule sizes. The values of the excess molar volume were correlated with the Redlich-Kister equation with the temperature dependence of the parameters as follows: where x 1 and x 2 is the ionic liquid and ethanol mole fraction, respectively; V E /(cm 3 ·mol −1 ) is the excess molar volume; A k is the temperature dependence parameters given as following: The root mean square error (RMSE) is expressed by the following: where n is the number of experimental points and p is the number of coefficients. The value of the Redlich-Kister parameters, A k , along with the standard deviation, are given in Table 11.
The combined standard uncertainty of excess volume of mixing (V E ) was determined using the error propagation law, using Equations (17) and (18) was calculated to be 0.008 cm 3 ·mol −1 . (17) and where M 1 , M 2 are the molar masses of IL and ethanol, respectively; ∆M 1 , ∆M 2 are the error of molar masses of IL and ethanol, respectively (∆M 1 = 0, ∆M 2 = 0); ρ 1 , ρ 2 are the densities of IL and ethanol, respectively; x 1 , x 2 is the composition of IL and ethanol, respectively; ∆x 1 , ∆x 2 is the uncertainty in composition determination of the mole fraction of IL and ethanol, respectively, m IL , m s is the mass of ionic liquid and solvent, respectively; ∆m IL , ∆m s is the weighing error (∆m = 0.0001 g); ∆ρ is the uncertainty of density measurement.  Points-experimental data; solid lines-correlation using equation (19) with parameters given in As expected, for each system under study, dynamic viscosity data decreases with an increasing temperature and increasing ethanol content. The comparison of dynamic viscosity data for an ethanolic solution under study at a temperature of 298.15 K is presented in Figure 8. It can be observed that the viscosity values for the tested systems decrease in the following series: The comparison of the dynamic viscosity value for pure dimethyl phosphate-based IL at a temperature of 298.15 K is graphically presented in Figure 9. Experiment shows that the dynamic viscosity value for pure iLs decreases in the following series: [C 1 [31]. Points-experimental, or literature density data; solid lines-calculated using Equation (19) with parameters given in Table 12; dashed lines-literature viscosity data for {LiBr (1) + Water (2)} system [55].
Within investigated temperature range, the dynamic viscosities for pure iLs vary from η = 17870 mPa•s at T = 293.15 K to 289.6 at T = 338. 15 [31]. Points-experimental, or literature density data; solid lines-calculated using Equation (19) with parameters given in Table 12; dashed lines-literature viscosity data for {LiBr (1) + Water (2)} system [55]. Temperature dependence of the dynamic viscosity for the binary systems under study was described using the following Andrade-type equation [56]: Temperature dependence of the dynamic viscosity for the binary systems under study was described using the following Andrade-type equation [56]: Parameter B is described by B = −E a R where R is the gas constant and E a is the flow activation energy.
Correlation parameters were calculated based on the relative residuals and the parameters were calculated by minimalized function given by the following: The root mean square deviation (RMSE) is expressed as following: The values of parameters A and B, along with RMSE, are given in Table 12. The calculation is graphically presented as solid lines in Figure 7.

Discussion
Thermodynamic and physicochemical properties of three pure ionic liquids and their ethanolic solution versus temperature and composition were presented in this study. Binary systems composed of IL and ethanol were analyzed for possible future use as working fluids in absorption refrigeration technology. In the studied systems, the ionic liquid would act as an absorbent and ethanol as a circulating agent. This is to search for alternative systems to the commercially used lithium bromide aqueous solution. An additional benefit would be the ability to operate the device at temperatures below 273.2 K due to the use of ethanol instead of water as the circulating medium. In the design of the new working fluid, it is desirable that the mixture exhibits negative deviations from Raoult's law (resulting in easier refrigerant absorption) and has as low density and viscosity values as possible, which allows easier mass and heat transfer. In this work, three binary solutions composed of [C 1  Thermodynamic and physicochemical properties, including vapor pressure, liquid density, and dynamic viscosity of binary systems composed of IL and ethanol, were experimentally determined as a function of temperature and composition. The experimental data was successfully correlated using the appropriate equations. Each system exhibits negative deviations from the ideal solution. . Based on liquid density data, the excess molar volumes were calculated and correlated using the Redlich-Kister equation with the temperature dependence of parameters. Since the main objective of the work is to search for working fluids for future use as an alternative to {LiBr + water} refrigeration systems, the experimental data presented were compared with those for an aqueous solution of lithium bromide, conventionally used in industrial-scale refrigeration technologies. The comparison shows that liquid density data for each binary system is lower than those for {LiBr + water} (see Figure 5). Dynamic viscosity for aqueous lithium bromide solution was determined within a narrow range of composition showing a steep course, and at higher concentrations of lithium bromide, the values would be diametrically higher than for the systems proposed in this work (see Figure 8). Resuming, the ethanol solutions of ionic liquid analyzed in this work, especially [N 1,2,2,2 ][DMP], exhibit a high potential for use as a working fluid in absorption cooling technology.

Materials
The ethanolic solutions of the dimethyl phosphate-based iLs, namely, 1-ethyl-1methylmorpholinium dimethyl phosphate (abbreviated as: with an initial mass fraction purity 0.970 was purchased from IoLiTec. The synthesis procedure of N,N,N-triethyl-N-methylammonium dimethyl phosphate was presented in our latest work [41]. Here, 1-ethyl-1-methylmorpholinium dimethyl phosphate was synthesized. The structure of the final product was analyzed by 1 H NMR and 13 C NMR spectra. A detailed description of the synthesis procedure and NMR analysis is given below. The NMR spectra are presented in Figures S7 and S8 in Supplementary Material (SM). The structures of the iLs tested in this work are presented in Table 13. To remove remaining volatile chemicals and to decrease water content before measurements, every IL was drained for 48 h in a vacuum drying oven (Binder, model VD 23) at a temperature T = 373 K and under reduced pressure (P = 4·10 −4 mbar) obtained by a vacuum pump (Vacuubrand RZ 6). The water mass fraction of the dried IL was determined using Karl-Fischer titration (model SCHOTT Instruments TitroLine KF). The sample description, including the purities, water content, and purification methods, is presented in Table 14. Table 13. The structures and basic information of ILs under study: molecular weight (M), liquid density (ρ), and dynamic viscosity (η) at temperature T = 313.15 K and pressure p = 0.1 mPa a .

Structure
Name The NMR spectra are presented in Figures S7 and S8 in Supplementary Material (SM). The structures of the iLs tested in this work are presented in Table 13. To remove remaining volatile chemicals and to decrease water content before measurements, every IL was drained for 48 h in a vacuum drying oven (Binder, model VD 23) at a temperature T = 373 K and under reduced pressure (P = 4•10 −4 mbar) obtained by a vacuum pump (Vacuubrand RZ 6). The water mass fraction of the dried IL was determined using Karl-Fischer titration (model SCHOTT Instruments TitroLine KF). The sample description, including the purities, water content, and purification methods, is presented in Table 14.  46.91 (N-CH3), 7.60 (C-CH3); Anion: 52.23 and 52.18 (CH3).
The NMR spectra are presented in Figures S7 and S8 in Supplementary Material (SM). The structures of the iLs tested in this work are presented in Table 13. To remove remaining volatile chemicals and to decrease water content before measurements, every IL was drained for 48 h in a vacuum drying oven (Binder, model VD 23) at a temperature T = 373 K and under reduced pressure (P = 4•10 −4 mbar) obtained by a vacuum pump (Vacuubrand RZ 6). The water mass fraction of the dried IL was determined using Karl-Fischer titration (model SCHOTT Instruments TitroLine KF). The sample description, including the purities, water content, and purification methods, is presented in Table 14.  Figures S7 and S8 in Supplementary Material (SM). The structures of the iLs tested in this work are presented in Table 13. To remove remaining volatile chemicals and to decrease water content before measurements, every IL was drained for 48 h in a vacuum drying oven (Binder, model VD 23) at a temperature T = 373 K and under reduced pressure (P = 4•10 −4 mbar) obtained by a vacuum pump (Vacuubrand RZ 6). The water mass fraction of the dried IL was determined using Karl-Fischer titration (model SCHOTT Instruments TitroLine KF). The sample description, including the purities, water content, and purification methods, is presented in Table 14. Thermophysical properties of pure iLs, including temperature (T m ) and enthalpy of melting (∆ m H), glass transition temperature (T g ), and heat capacity at the glass transition temperature (∆ g C p ), as well as temperature (T tr ) and enthalpy (∆ tr H) of (solid + solid) phase transition, were determined by DSC 1 STAR e System (Mettler Toledo) calorimeter, which used differential scanning calorimetry (DSC) technique. The calibration of the apparatus was carried out by measuring the samples of 99.9999 mol% purity indium and high-masspurity n-heptane (Sigma-Aldrich (St. Louis, MO, USA), ≥99.5%), n-octane (Sigma-Aldrich, ≥99%), n-decane (Sigma-Aldrich, ≥99%), ethylbenzene (Sigma-Aldrich, ≥99%), cyclohexane (POCH, ≥99.5%), n-dodecane (Acros Organics, ≥99%), n-octadecane (Aldrich, ≥99%), naphthalene (Acros Organics, ≥99%), and water (Millipore, κ < 0.05 mS·cm −1 ). Calibration measurements were made at the heating/cooling rate of 5 K·min −1 in a temperature range from T = (180 to 430) K. The uncertainties are as follows: u(T) = 0.3 K, u(∆H) = 3.3 J·g −1 . Measurements of all examined IL samples were performed in heating mode at the heating rate of 5 K·min −1 . A sample of the tested ionic liquid weighing about 10 mg was placed in an aluminum pan and an empty hermetic aluminum pan was used as a reference. The apparatus includes a liquid nitrogen cooling system, and the measurements were made in an inert atmosphere with a nitrogen flux of about 200 mL/min. The experiments were carried out within the temperature range from (173.15 to 373.15) K. The experimental data were analyzed using STARe DB V12.00 software (Bhopal, India).

(Vapor-Liquid) Phase Equilibria Measurements
The isothermal vapor-liquid phase equilibrium (VLE) measurements were performed using an ebulliometric method, where the main part of the apparatus is a specially designed ebulliometer [57]. The mixture of ionic liquid and ethanol placed in the device is in continuous movement forced by the operation of the Cottrell pump. The superheated two-phase mixture gets decompressed, and it is thrown through the tube onto the socket of the thermometer. It is assumed that the expansion in the equilibrium chamber causes the loss of excess heat of the superheated liquid, which is used to evaporate the additional amount of liquid. As a result, the equilibrium temperature is established on the walls of the thermometric socket under the conditions of pressure in the system. By changing the pressure in the system, one can set the temperature of the measurement. Measurements were made at the following three constant temperatures: 348.15, 338.15, and 328.15 K. In the equilibrium chamber, the two-phase mixture is separated into the following two streams: a steam flow and a liquid flux. Ionic liquids have a negligibly low vapor pressure, so the steam flow consists only of ethanol. Before the two streams are combined, samples can be taken from the gas phase and liquid phase reservoirs. Earlier, the steam flow enters the condenser. A very important role is played by thorough mixing of the combined streams. For this purpose, glass tubes were designed in an appropriate way and stabilizing system comprising the isolated container with a volume of 50 dm 3 enabled the pressure to be kept constant within 0.1 kPa and to dampen the pressure fluctuations caused by the bumping of the liquid boiling in the ebulliometer or by the variation of the temperature of the surroundings was implemented. The equilibrium temperature was measured with a resistance thermometer (type P-550, Roth, Germany) with a precision of 0.01 K. The pressure was measured with the precision of 0.1 kPa by a tensiometric vacuum meter (type CL 300, ZEPWN, Poland). The thermometer and the manometer were calibrated by measuring the boiling points as a function of pressure for n-octane, ethanol, and water and compared to values obtained from the literature [58]. The uncertainty was at the level of u(p) = 0.2 kPa and u(T) = 0.05 K. The composition of samples taken from the ebulliometer was determined densimetrically based on previous density measurements in two-component systems using the Anton Paar GmbH 4500 vibrating-tube densimeter (Graz, Austria) with an accuracy of 1·10 −5 g·cm −3 at each temperature. Only the liquid phase was sampled because, as previously mentioned, the gas phase consisted only of pure ethanol. A calibration curve of density vs. mole fraction of IL was made and the uncertainty in the mole fraction composition was better than 2·10 −3 . The VLE measurement error was caused by an error related to incorrect indications of the thermometer, error related to incorrect indications of the manometer, error resulting from the calibration curve of the manometer, error related to the accuracy of determining the mole fraction of the liquid phase, error related to other factors influencing the determination of the equilibrium temperature, such as the following: imperfection of mixing inside the measuring cell, which creates a concentration gradient, disturbance of the equilibrium conditions during sampling, or impurities present in the sample. The total measurement error is the sum of the factors mentioned above. The combined uncertainty of the method used for the VLE estimation is larger than the instrument error and was estimated at 0.5 kPa.

Density Measurement
The liquid density of pure ILs and their ethanolic solutions were determined at a temperature range from T = (293.15 to 338.15) K with an increment of 5 K at ambient pressure.
The densities were measured on an Anton Paar GmbH 4500 densimeter using vibrating tube method. Measurements were made at different temperatures with a built-in thermostat. The precision in the temperature control (internally of 0.01 K) is provided by two integrated Pt 100 platinum thermometers. The apparatus was calibrated at atmospheric pressure using double-distilled degassed water and air. The densimeter is precise to within 1·10 −5 g·cm −3 , and because of the purity of IL, estimated standard uncertainty of the density measurement, u(ρ) is better than 5·10 −3 g·cm −3 .

Dynamic Viscosity Measurements
Viscosity measurements for pure ILs and their ethanolic solution were carried out using DVNext Wells-Brookfield Cone Rheometer (Middleborough, United States of America). The experiment was performed within the temperature range from T = (293.15 to 338.15) K with an increment of 5 K. The apparatus consists of torque measuring system, where a calibrated beryllium-copper spring is the main part. The spring is connected to the drive mechanism of a rotating cone, and it senses the resistance to rotation caused by the presence of a liquid sample between the cone and a stationary flat plate. The resistance to the rotation of the cone produces a torque that is proportional to the shear stress in the fluid. Then, the reading is converted to centipoise units from pre-calculated range charts. The tested pure ionic liquids and their solutions with ethyl alcohol are Newtonian liquids, which means that viscosity does not depend on the shear rate. It was checked before every measurement. The system was previously calibrated to the standards by the manufacturer, and calibration was verified using appropriate standards. The mean standard deviation of viscosity was determined based on standard measurements, and the relative uncertainty, u r (η) value, was determined to be 0.03. The apparatus is accurate to within 1.0% of the full-scale range reproducibility is within 0.2%. The working temperature range is from 0 • C to 100 • C. Two cones were used for viscosity measurements. One for measurements above 250 mPa·s with a cone radius of 0.012 m and a cone angle of 1.5 • , and the other for measurements below 250 mPa·s, with a radius of 0.024 m and a cone angle of 0.8 • . The gap between the cone truncation and the plate was 12.7·10 -6 m.  Table 7; dashed lines-ideal solution; Figure S2 Table 7; dashed lines-ideal solution; Figure S3. Temperature and composition dependence of liquid density data for {[C1C2PIP] [DMP] (1) + Ethanol (2)} system as a function of (a) temperature for different composition,  Table 11. Figure S5. Experimental and calculated dynamic viscosity data for {[C1C2PIP] [DMP] (1) + Ethanol (2)} binary system as a function of (a) temperature for different IL mole fraction, x 1 : , 1.0000; , 0.8993; ♦, 0.7968; , 0.7031; , 0.6007; , 0.5028; , 0.4027; , 0.3001; ∆, 0.2001; •, 0.1001; , 0.0000. Points-experimental data; solid lines-correlation using Equation (19) with parameters given in Table 11. (b) Composition at different temperature, T: , 293.15 K; ♦, 303.15 K; •, 313.15 K; , 323.15 K; , 333.15 K. Points-experimental data; solid lines-guide to the eye; Figure S6. Experimental and calculated dynamic viscosity data for {[N1,2,2,2][DMP] (1) + Ethanol (2)} binary system as a function of (a) temperature for different IL mole fraction, x 1 : , 1.0000; , 0.8987; ♦, 0.7991; , 0.6988; , 0.5986; , 0.4998; , 0.4004; , 0.3011; ∆, 0.1999; •, 0.0998; , 0.0000. Points-experimental data; solid lines-correlation using Equation (19) with parameters fiven in Table 11